Field of Invention and Prior Art
Sterile disposable covers or caps for the tip of a tonometer, which is in practice pressed against the surface of the cornea of an eye, to prevent contamination of the cornea of a patient by transmission of contaminants such as bacteria or the like from one patient to the next during the normal employment of a tonometer.
Literally millions of tests to determine intraocular pressure indicative of glaucoma or related diseases of the eye, or tendencies thereto, are conducted yearly by opticians, optometrists, and their technical assistants. The device employed in the making of such observations is a tonometer. According to normal use of a tonometer, the operator of the same peers through the device and adjusts the lens at the end of the tip thereof against the cornea of the test subject in order to effect a specific diameter or circumference of a portion of the cornea which is flattened against the lens of the tonometer tip. When the necessary diameter or circumference of the area of flatness of the cornea against the lens has been attained, a blast of air is released against the flattened portion of the cornea, whereupon a reading is obtained which allows determination of the intraocular pressure within the eyeball.
In such a determination, the operator must be able to see through the lens of the tonometer tip in order to be certain that the necessary flattened area of the cornea for performance of the test has been attained, and calibrations are usually provided on the surface of a rotatable frustoconical-tonometer tip, which is rotatable upon a base member, for enabling the operator to make necessary adjustments in a particular case and
e to enable a proper reading of the interocular pressure from employment of the device. The present invention has nothing to do with the normal operation of a conventional tonometer or tonometer tip, but seeks to provide a means for preventing transmittal of contamination of any kind, but most especially in the form of microorganisms such as bacteria or the like, from one patient to a succeeding patient during the normal course of tonometery examinations.
One of the foremost problems encountered in the use of a tonometer for such examinations is just the type of contamination mentioned. If one tested patient has a cornea which is contaminated with bacteria, and the lens of the tonometer tip is not adequately cleaned between employment of the device on succeeding patients, transmittal of the disease from one patient to a succeeding patient is not only likely, but in fact often occurs. The problem of adequately cleaning and sterilizing the lens of the tonometer tip between usage of the device upon a succession of patients is demanding and is often overlooked or inadequately carried out, so that it is not uncommon for a patient having recently undergone a tonometer test to develop "red eye", a bacterial and/or viral infection transmitted from one patient to another through the medium of contamination of or on the tonometer tip lens. This problem has been recognized and various review articles have appeared setting forth the problem, without however suggesting any practical solution thereto other than a more careful attention to the sterilization of the tonometer tip and/or more complete sterilization of the tonometer tip between its use on successive patients. Among some of the articles which have appeared are the following:
Viability of Herpes Simplex Virus Type 1 on the Applanation Tonometer, Ventura LM; Dix RD, AM J Ophthalmol 1987 Jan 15; 103 (1): 48-52.
"Sterilization of Impression Tonometers Using a Sterilization Ring. Virological Studies", Odkazanie tonometru impresvjnego przy uzyciu pierscienia sterylizacyjnego. Badania wirusologiczne, Jedrzejewski D; Gerkowicz M, Klin Oczna 1985 Aug; 87 (8): 315-317.
Disposable Film Cover for the Tip of Goldmann's Tonometer, Nardi M; Bartolomei MP; Falco L; Carelli F, Graefes Arch Clin Exp Ophthalmol 1985; 223 (2): 109-110.
Tonometer Disinfection and Viruses, Nagington J; Sutehall GM; Whipp P, Br J Ophthalmol 1983 Oct; 67 (10): 674-676.
"Septic Potential of Tonometers and Triple-mirror Glasses", Etude de la septicite des tonometres et des verres a trois miroirs, Rossazza C; Bertrand F; Vargues R, Bull Soc Ophtalmol Fr 1983 Mar; 83 (3): 411-412, 415-416.
"Modified Version of a UV Sterilizer to Disinfect Goldmann Tonometer Heads, Gonioscopes and Fundus Contact Lenses", Modifikation eines UV-Gerates zur Desinfektion bulbusberuhrender ophthalmologischer Instrumente, Wizemann A, Klin Monatsbl Augenheilkd 1982 Jul; 181 (1): 40-41.
Hepatitis B Surface Antigen in Human Tears, Darrell RW; Jacob GB, Arch Ophthalmol 1978 Apr; 96 (4): 674-676.
Contamination of Applanation Tonometer Prism, Norn MS; Thomsen F, Acta Ophthalmol (Copenh) 1968; 46 (4): 712-720.
The problem is widespread and has been particularly recognized in the Nardi et al. publication entitled "Disposable Film Cover for the Tip of Goldmann's Tonometer", appearing in Graefe's Archive of Clinical and Experimental Ophthomology, cited in the foregoing, but the proposal advanced by those authors is unacceptable in practice and leaves much to be desired. In their proposal, a drop of distilled water must be placed on the front surface of the double prism of the tonometer, and a polyvinyl chloride (PVC) film disk, fixed to a circular rigid mount and perforated about its internal circumference, must then be held by the mount and pressed against the front surface of the double prism in order to apply an even film of liquid between the PVC film and the double prism itself. Then, by further traction and a twisting movement on the mount, the film is torn at the level of the perforations, and caps the double prism with a thin transparent film, whereafter the tonometer tip or prism can be remounted on the tonometer. After employment in tonometry, the film must then be removed with forceps. Care must be taken so as not to impair its sterility, especially before use. This proposed solution to the problem is, however, much too complex and delicate for practical use and the major contribution of this article is to point up the problem of sterility with the tonometer tip and the prism located therein, which is the problem solved by the device of the present invention. According to Nardi et al., the methods previously suggested for solution of the problem have at least one of the following drawbacks: (1) they are unreliable, especially in the case of viral infection; (2) they are not practical; (3) they are time consuming; (4) they can damage the double prism (citing additional publications). Nardi's proposal falls in at least category (2).
It would, accordingly, be highly desirable to have available an economical and readily-utilizable means for ensuring that the portion of the tonometer which comes into contact with the cornea of the eye of a patient being tested therewith is sterile and free from contamination, especially due to use of the tonometer upon a preceding patient, and the present invention provides just such a means in the form of a disposable anticontamination tonometer tip cover or cap, which does not in the slightest interfere with the normal operation of the tonometer but which, on the other hand, not only avoids the tedious problem of sterilization and adequate sterilization of the lens of the tonometer tip between patients, but moreover provides a practical and use-effective means for ensuring sterility of the portion of the tonometer which comes into contact with the cornea of every patient tested therewith.